What does the Win7-installation to my USB-data-drive?

Hello,
I am just installing windows 7 aon my Samsung Q45, which previosly ran on Vista.

Now I am wondering, what the hack Win7 is performing on my attached data-drive (Simple-Drive 2TB, USB 2.0) which I left accidentally connected to my lappy.

It says "functions are beeing installed" - and the USB-drive works like cracy, for about 20 minutes by now!
Does it indicate the files, or even mix s.th up?

If I had not let it plugged in bevore installation, win7 would certainly run by now! And the drive is not exclusively for this PC, so what does Windows do with it? It should absolutely ignore my data-drive, for it will be anyways migrated to a NAS in some weeks.

But I do not dare to plug the USB off by now - what to do? Relax?

Someone who can expain this behavour? THX!

After some time of waiting Win7 finished, and now runs "normal".

Still I am wondering, what it did on my USB-data-drive, for there where no significant changes obvious.

Can s.o. explain, why the installation took such a long (aprox. 30 minutes) and intense (the HD was all the time running and clicking) prozess? Does Win7 look for Malware or prevoiuos installations?

Thanks, supi